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AD7829BRU-1REEL7 データシート(PDF) 11 Page - Analog Devices |
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AD7829BRU-1REEL7 データシート(HTML) 11 Page - Analog Devices |
11 / 20 page AD7829-1 Rev. 0 | Page 11 of 20 A suggestion is to tie CONVST ANALOG INPUT to VDD or DGND through a pull-up or pull-down resistor. A rising edge on the CONVST pin causes the AD7829-1 to fully power up. For applications where power consumption is of concern, the automatic power- down at the end of a conversion should be used to improve power performance (see the The AD7829-1 has eight input channels. Each input channel has an input span of 2.5 V or 2.0 V, depending on the supply voltage (VDD). This input span is automatically set up by an on-chip “VDD detector” circuit. A 5 V operation of the ADCs is detected when VDD exceeds 4.1 V, and a 3 V operation is detected when VDD falls below 3.8 V. This circuit also possesses a degree of glitch rejection; for example, a glitch from 5.5 V to 2.7 V up to 60 ns wide does not trip the VDD detector. Power vs. Throughput section). If the AD7829-1 is operated outside normal VDD limits (for example, a brown-out), it may take two conversions to reset the part once the correct VDD has been established. SUPPLY 4.5V TO 5.5V 10µF 0.1µF VDD VREF VMID VIN1 1.25V TO 3.75V INPUT VIN2 VIN8 AGND DB0 TO DB7 EOC RD CS CONVST A0 A1 A2 PARALLEL INTERFACE µC/µP AD7829-1 DGND 2.5V AD780 The VMID pin is used to center this input span anywhere in the range of AGND to VDD. If no input voltage is applied to VMID, the default input range is AGND to 2.0 V (VDD = 3 V ± 10%), that is, centered about 1.0 V; or AGND to 2.5 V (VDD = 5 V ± 10%), that is, centered about 1.25 V. When using the default input range, the VMID pin can be left unconnected; or, in some cases, it can be decoupled to AGND with a 0.1 μF capacitor. If, however, an external VMID is applied, the analog input range is from VMID − 1.0 V to VMID + 1.0 V (VDD = 3 V ± 10%), or from VMID − 1.25 V to VMID + 1.25 V (VDD = 5 V ± 10%). The range of values of VMID that can be applied depends on the value of VDD. For VDD = 3 V ± 10%, the range of values that can be applied to VMID is from 1.0 V to VDD − 1.0 V and is 1.25 V to VDD − 1.25 V when VDD = 5 V ± 10%. Table 5 shows the relevant ranges of VMID and the input span for various values of VDD. Figure 7. Typical Connection Diagram Figure 9 illustrates the input signal range available with various values of VMID. ADC TRANSFER FUNCTION The output coding of the AD7829-1 is straight binary. The designed code transitions occur at successive integer LSB values (that is, 1 LSB, 2 LSBs, and so on). The LSB size is equal to VREF/256 (VDD = 5 V), or the LSB size is equal to (0.8 VREF)/256 (VDD = 3 V). The ideal transfer characteristic for the AD7829-1 is shown in Table 5. VMID Internal VMID Ext Minimum VMID Ext Maximum VDD VIN Span VIN Span 5.5 1.25 4.25 3.0 to 5.5 1.25 0 to 2.5 Figure 8. 11111111 111...110 111...000 10000000 000...111 000...010 00000000 (VDD = 5V) 1LSB = VREF/256 (VDD = 3V) 1LSB = 0.8VREF/256 000...001 1LSB VMID (VDD = 5V) VMID – 1.25V (VDD = 3V) VMID – 1V VMID + 1.25V – 1LSB VMID + 1V – 1LSB ANALOG INPUT VOLTAGE Figure 8. Transfer Characteristic 5.0 1.25 3.75 2.5 to 5.0 1.25 0 to 2.5 4.5 1.25 3.25 2.0 to 4.5 1.25 0 to 2.5 3.3 1.00 2.3 1.3 to 3.3 1.00 0 to 2.0 3.0 1.00 2.0 1.0 to 3.0 1.00 0 to 2.0 2.7 1.00 1.7 0.7 to 2.7 1.00 0 to 2.0 |
同様の部品番号 - AD7829BRU-1REEL7 |
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同様の説明 - AD7829BRU-1REEL7 |
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